The canonical paper on this topic is Edmund Schulman's classic "Longevity under Adversity in Conifers" (1954)[1]

When I worked in a tree-ring dating lab, we always sought out the harshest local environments in a region and then at a given site, the harshest micro-environments (typically water limited but fire protected) because that's where you find the most ragged, pathetic, and correlatively oldest trees around with the most climate sensitivity in their ring patterns. This makes the ideal trees to date and build climate chronologies from.

[1]: https://sci-hub.tw/10.2307/1682970

10k above sea level would also put the tree well above major jet streams that carry pollution. A similar pattern occurred with a group in (I think) Norway, that were said to have the "fountain of youth", but it just simply turned out they were out of the way of pollution.

Sorry to nitpick, but I think you might have confused 10k feet vs 10k meters (10kms). The grandparent was using feet. 10k feet is about 3kms, the height of a medium sized mountain. 10kms is about the height of Everest, whose peak does not have trees at all. I don't know at what elevation trees stop appearing, but it would be well under 10kms.

> I don't know at what elevation trees stop appearing

This is known as the "tree line", and varies a lot based on particular location (due to sun exposure, climate, and plant species). Here's a wikipedia article which outlines where the tree line: https://en.wikipedia.org/wiki/Tree_line . Summary is that the treeline is rarely above 12k feet (3500m), though in Bolivia it gets all the way up to 17k feet (5200m)!!

You are probably correct w.r.t. the main flow of the jet stream being far in excess of the highest tree lines in the world. The jet stream's main flow is usually 30k feet (10k meters) or higher.

>but is the goal to keep trees alive as long as possible?

For some trees, being 100year old means that the trees are in their late teens/twenties/thirties (source above book). With that in mind, the answer to above question becomes somewhat difficult.

You are also applying mammalian standards to a plant. Trees may indeed be capable of living a very long while, but that does not mean that such lives are normal. A tree can live a full and productive life, reproducing and spreading many times, centuries before its total lifespan. There is also some speculation that trees may be immortal, that if their growth is artificially managed that they may just never have to die. Plants are different than mammals. They don't all have the same definitive life cycles.

For many cities, the goal is a healthy and sustainable urban canopy. Arboriculture has advanced a lot in the last hundred years, and we've made a lot of mistakes.

Eg, inappropriate species like Big Leaf Maple in inappropriate locations, like under power lines. Bad pruning practices. Planting monocultures (Elm). Boxing in roots.

As sick trees come down, better practices can lead to better trees for the next generation.

For some common species, 100 years is downright old, and reaching the end of their natural life anyways.

> So the urban tree does die "young", but is the goal to keep trees alive as long as possible?

In an urban area, it should be. Not only does it cost money to have to replace a dead tree, but a dead (or even not-quite-yet-dead) tree runs the risk of falling over, which means damaging property, blocking streets/sidewalks, or even injuring/killing animals (including humans).

> is the goal to keep trees alive as long as possible?

climate change and economic reasons would support this goal.

> Perhaps we should trim our urban trees more aggressively.

Killing it much faster